Influence of grain refiner addition on the precipitation of Fe-rich phases in secondary AlSi7Cu3Mg alloys

The effect of grain refiner addition on the precipitation of Fe-rich compounds in secondary AlSi7Cu3Mg has been studied. Thermal and metallographic analysis techniques have been used to examine the formation of Fe-bearing intermetallics. The results show that grain refinement with AlTi5B1 can alter the precipitation sequence of Fe-rich phases. In non-grain refined alloy and grain-refined alloy with AlTi10, two different Fe-rich phases, a-Al15(Fe,Mn)3Si2 and p-Al8Mg3FeSi6, form, whereas, with AlTi5B1 addition, the b-Al5FeSi phase also tends to crystallize, nucleating on TiB2 particles. It has also been demonstrated how at high cooling rates, the b-Al5FeSiinvolved reactions occur more preferentially, when compared to a-Al)15(Fe,Mn)3Si2 phase. This crystallization behaviour is explained in terms of phase diagram relationship and the nucleation kinetics of competing a-Al)15Si(Fe,Mn) )3Si2 and b-Al5FeSi phases.